To modify a Drupal site.

Have a website on Drupal 7 isrii , updated a week ago. This is the car.
Required on the website to make an online service booking type as here namely : the User enters and can be recorded to the nearest 25 days, With entry fields : name, phone number, make of car, description of the problem ( what to do), the minimum captcha type 3 2= .... . The intervals of administration of cars in service is charged by the site administrator ( for example, the reception interval of 10 minutes), when submitting an application for this time no more entries, the site Admin can cancel the entry and the time will be free or Vice versa to take a while, thus giving him the record. In any case you have to write requirements specification.
From The Contractor:
1. Time.
2. Budget.
3. Questions.